Fermi-surface reconstruction in the cuprate superconductor YBCO via the thermal Hall effect

We recently showed that the thermal conductivity $\kappa_{xx}$ can be used to directly measure the upper critical field H$_{c2}$ in cuprate superconductors [1]. Here we show that the thermal Hall conductivity $\kappa _{xy}$ can be used to probe the nature of the carriers in these materials. We present a study of $\kappa_{xy}$ in YBCO at a doping p $=$ 0.11, as a function of magnetic field up to 35 T down to low temperature. The fact that $\kappa_{xy}$ is negative above H$_{c2} \quad =$ 24 T confirms the presence of an electron-like pocket in the normal-state Fermi surface [2], the result of a reconstruction caused by the emergence of charge order at low temperature [3]. We show how the Fermi-surface reconstruction evolves as a function of field and temperature. [1] G. Grissonnanche \textit{et al.}, arXiv:1303.3856 (2013). [2] D. LeBoeuf \textit{et al}., Nature 450, 533 (2007). [3] F. Lalibert\'{e} \textit{et al}., Nature Communications 2, 432 (2011).